Here's how the deck looks with the upgrades added: Also to pre-emptively address some comments: one direction that you can take the upgrades is to really lean into Sliver Gravemother's encore ability and turn the deck into a straight-up Encore deck -- Buried Alive and Entomb cards to put slivers into your graveyard, Convergence of Dominion and Zirda, the Dawnwaker to make encore cost less (though PSA Training Grounds doesn't work, I see people suggesting it but sorry no), Mondrak, Glory Dominus to double the encore tokens, Sundial of the Infinite to keep the encore tokens permanently -- that sounds sweet and all but you'd need to do a massive rework of this entire precon, turning it from a Go Wide Sliver Combat deck to Sliver Reanimator essentially
Holiday sets or special sets dont have booster boxes
Its probably the first thing that sticks out
Temur Adventures, by contrast, usually has Obosh, the Preypiercer as the companion, which means that it can't even run those even-costed spells if it wanted to
Despite being printed in four different sets, this keeps the price of Dual Lands in step with Reserved List cards with much smaller print runs